In posting questions on MSE, I find that, if a question is not answered within a day or so, it will not receive an answer at all. Typically, I have waited for several weeks before cross-posting such a question on MathOverflow, where usually it gets a good response. From my experience, however, there seems to be no point in waiting so long, and a wait of one week is plenty to confirm that a question will not be answered.
I normally post a question on MSE first because I expect or hope that it will get an answer here. Sometimes it turns out that a question is more suited to MO, but generally I can't tell this in advance—perhaps there is a ready answer that I missed, and I don't want to bother the MO forum with off-topic material.
Thus, to formulate a specific question: Is it is considered acceptable behaviour to post on MO a question that received no answer on MSE within a week? If not, what would be deemed an appropriate waiting period?